regulator: s2mps11: Fix GPIO descriptor initialization

GPIO descriptor array must be zero initialized to ensure that core will
properly handle also the case when no external GPIO pin is defined.

Fixes: 1c984942

 ("regulator: s2mps11: Pass descriptor instead of GPIO number")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>